I. FIELD OF THE INVENTION
The present invention relates to a system for controlling the opening times of fuel injectors in an electronic fuel injection system for a heat engine.
II. DESCRIPTION OF THE PRIOR ART
As is known, in electronic fuel injection systems for heat engines there is an electronic control unit which, in dependence on signals which it receives from various sensors (principally the revolution counter sensor, the sensor detecting the phase of the engine, and sensors detecting the intake manifold pressure and intake air temperature), determines, for example, the density of the air in the induction manifold (i.e., intake manifold pressure) and the speed of revolution of the engine, and calculates the timing and duration of injection of fuel to the injectors, and the ignition advance, based upon tabulated values in a computer memory. Such injectors can be individually provided for each cylinder, disposed downstream of the butterfly valve, or can be provided as a single injector located either upstream or downstream of the butterfly valve. The quantity of fuel delivered to each injector at each opening cycle is therefore variable within wide limits depending on the operating conditions of the engine. Moreover, it must be observed that, as can be seen from FIG. 2, the characteristic curve which relates the opening time of the injector and the quantity of fuel delivered through the injector itself is substantially linear in only a central section lying between the opening times A and B, and that the linearity is not guaranteed for shorter times (less than MIT, defined as the minimum acceptable injection time) and for very small rest periods of the injector between successive operating periods (less than MIOT, the minimum acceptable injector closure time, defined with respect to the repetition period of operation PI). The quantity IOT is the intrinsic delay time of the injector, dependent on the supply voltage. Thus, when the central control unit determines an injector operating time outside the range of linearity, the operating conditions of the system become inefficient.